Can anyone pls clarify the maximum Transmit power of SXT 2?

As per specs the chip has 32dbm max transmit power and the antenna is 10dbi. So the total max transmit power out of the antenna is 42db=15.85watts?

Am I correct?

No. And yes.
Power still remain 32dbm.
EIRP=power+antenna

Equivalent Isotropically Radiated Power (EIRP) is the product of transmitter power and the antenna gain in a given direction relative to an isotropic antenna of a radio transmitter

I am interested at the power level that is "leaving" the antenna.. That must be ~ 16 watts.... right?

Yes, total are about 15 w

yes theoretically at 6mbps you have 32dbm of tx power + 10dbi of antenna gain= 42 dbm = 15848mw EIRP

but at mcs 7 you have 25dbm of tx power + 10dbi of antenna gain= 35dbm = 3162mw EIRP

keep in mind at 2.4ghz there is a lot of interference and Fresnel zone is bigger